A hydraulic excavator that is one type of construction machine includes a self-propelled lower travel structure, an upper swing structure swingably provided on an upper side of this lower travel structure, and a work device coupled to this upper swing structure. The work device includes, for example, a boom rotatably coupled to the upper swing structure, an arm rotatably coupled to the boom, and a bucket rotatably coupled to the arm. In addition, a plurality of hydraulic cylinders (specifically a boom cylinder, an arm cylinder, and a bucket cylinder) drive the boom, the arm, and the bucket to rotate. Each hydraulic actuator is driven by a hydraulic fluid supplied from a hydraulic pump via, for example, a hydraulic pilot-type directional control valve.
Types of operation devices operated by an operator include a hydraulic pilot-type operation device and an electric lever-type operation device. The hydraulic pilot-type operation device has a plurality of pilot valves corresponding to operation directions from a neutral position of an operation lever and each generating a pilot pressure in response to an operation amount of the operation lever. Each pilot valve outputs the pilot pressure to an operation section (pressure receiving section) of the corresponding directional control valve to drive the directional control valve.
The electric lever-type operation device has a plurality of potentiometers corresponding to operation directions from a neutral position of an operation lever and each generating an operation signal (electrical signal) in response to an operation amount of the operation lever. A controller generates a command current in response to the operation signal from each potentiometer, and outputs the command current to a solenoid section of a corresponding solenoid proportional valve to drive the solenoid proportional valve. The solenoid proportional valve generates a pilot pressure proportional to the command current, and outputs the pilot pressure to the operation section of the corresponding directional control valve to drive the directional control valve.
It is known that a driving system including the electric lever-type operation device described above, the controller, the solenoid proportional valves, and the directional control valves delay in an initial response of each hydraulic actuator (in other words, in a response of each hydraulic actuator at a time of starting to operate the operation lever from the neutral positions thereof), compared with a driving system including the hydraulic pilot-type operation device described above and the directional control valves. This is because signal generation of the operation device, signal output from the operation device to the controller, signal processing by the controller, and current output from the controller to the solenoid proportional valves cause a time delay. This is also because although a spool of each solenoid proportional valve is not completely closed yet right after the operation lever returns to the neutral position, the spool of the solenoid proportional valve is completely closed and the spool delays in an initial motion when a state in which the operation lever is at the neutral position continues.
Meanwhile, Patent Document 1 discloses a driving system that includes an electric lever-type operation device, a controller outputting a command current in response to an operation signal from the operation device, and solenoid proportional-type directional control valves each driven by the command current from the controller. In addition, the controller corrects the command current to the directional control valve in such a manner that the command current is higher than a target current corresponding to an operation amount of the operation device for preset predetermined time at a time of starting to operate the operation device from a neutral position thereof.